Many types of handheld electronic devices—such as cell phones, personal digital assistants (PDAs), Global Positioning System (GPS) receivers, or other radio receivers—can be used to provide a number of location based services. For example, a shopper in a mall may be able to receive information on and directions to stores near her having a sale on a particular item for which she is searching based on the device, e.g., a cell phone, “knowing” her current location inside the mall. Or, she may be able to shop with friends who can mutually keep track of each other's locations, or any number of other endless possibilities may exist based on the devices' being able to accurately locate their own positions, in other words, to accurately navigate.
To use the cell phone example, the provision of location based services may depend on the cell phone having the ability to make use of navigation and timing signals provided by various existing satellite navigation systems, such as GPS. In many situations where the satellite signals may be occluded, however, these satellite systems typically do not provide sufficiently satisfactory system performance, e.g., signal power, to enable reliable location based services. For example, navigation satellite signals may suffer extreme attenuation inside buildings, such as in the shopping mall example given above, and other high-blockage environments, e.g., locations surrounded by building structures. In addition, navigation satellite signals may be subject to other effects, such as rain fade; multipath distortion, e.g., around tall buildings; jamming, e.g., in military contexts; and attenuation through deep foliage.
Some location based service systems and navigation systems have attempted to address indoor navigation deficiencies by the use of various approaches, for example, inertial navigation systems, specialized beacons, and highly sensitive GPS systems. Inertial navigation systems, however, drift and are expensive. Beacons require specialized fixed assets that are expensive and not standardized, thus having only specialized utility. Sensitive GPS systems generally do not perform to user expectations due to their continuing inability to reliably overcome the weakness of the GPS signals in indoor environments. Other navigation approaches based, for example, on cellular telephone or television signals typically lack vertical navigation information.
As a result, there is a need for improving the sensitivity of navigation signal, e.g. GPS signal, reception for handheld devices, such as cell phones, PDAs, GPS navigators, or other portable radio receivers so that indoor location based services and navigation can be reliably provided. In addition, there is a need for providing such navigation signal reception sensitivity within the narrow constraints (e.g., limited volume, weight, and power dissipation requirements) of handheld devices.